Top Foal-Related Studies of 2012-'13

Researchers learned that hospitalization as a foal does not appear to affect sales price or buy-back rate at auction.

Photo: Anne M. Eberhardt/The Horse

Even though they're small in stature, foals can have some big health problems. And researchers around the world are continually working to better understand these health problems and find more effective ways to treat them. At the 2013 Society for Theriogenology Conference, held Aug. 7-10 in Louisville, Ky., Chris Sanchez, DVM, PhD, Dipl. ACVIM, associate professor at the University of Florida College of Veterinary Medicine, reviewed some of the top research papers published in the last year focusing on foal health.

The first study Sanchez described aimed to answer an "age-old" question: is it worth it, financially, to hospitalize and treat sick neonatal foals? While several research papers have evaluated the future racing performance of hospitalized Thoroughbred foals, she pointed out that some breeders don't necessarily want to know if the foal will race successfully after treatment. In many cases, they want to know if the foal will sell at auction.

To determine if hospitalized foals presented for public auction sell for a comparable price to controls, a pair of Irish researchers evaluated 63 foals hospitalized before reaching 125 days of age (roughly four months). Of those horses, 19 were presented to be sold as weanlings, 39 as yearlings, and five as 2-year-olds. Using other sales horses (the three horses presented to the same sale immediately before and immediately after the subject) as controls, the team found that hospitalization as a foal does not appear to affect sales price or buy-back rate at auction.

"The bottom line from their study was that if foals made it to the sales, they did not have a significant difference in buy-back rate or sales price, relative to controls," Sanchez said. "It's a quick, simple study, but it's really good information."

Sanchez then delved into a study addressing the adage that hospitalized neonatal foals receive an anti-ulcer prophylactic treatment because it won't hurt them. The researchers reviewed the medical records of 1,102 foals without diarrhea as a presenting complaint admitted to three university hospitals in the United States and three private veterinary clinics around the world. The team looked for what (if any) anti-ulcer treatment was administered, if diarrhea developed while the foal was hospitalized, the presence of gastric ulceration, duration of hospital stay, short-term outcome, and other factors.

The team found three factors associated with diarrhea development in the hospital:

Age (foals older than 1.5 days at admission were more likely to develop diarrhea);

Hospital stay duration (foals that remained in the hospital for a week or more were more likely to develop diarrhea); and

Anti-ulcer medication administration (foals that received prophylactic treatment had an increased risk of developing diarrhea).

Additionally, Sanchez said, anti-ulcer treatment was not associated with the presence of gastric ulceration, meaning foals were likely to have an ulcer regardless of whether they had been treated with anti-ulcer medications.

"I often advocate strongly against prophylactic use in neonates," she said. "Gastric acid is there for a reason, including protecting the rest of the gastrointestinal tract from bacteria entering the stomach."

She also noted that some medications used to treat other ailments require an acidic environment to be effective. Combining these drugs with anti-ulcer medications designed to raise the stomach's pH effectively nullifies any effect they'll have on helping the foal's ailment heal.

"There's no evidence to support prophylactic use of anti-ulcer meds unless the foal has signs of ulcers," she stressed.

Next, Sanchez described a study that shed some new light on the hypothalamic pituitary adrenal (HPA) axis, which regulates stress hormones in the body, and its role in young foals. In healthy, sick nonseptic, and septic foals, the researchers measured:

Total and free thyroxine (T4, one of two iodine-containing hormones the thyroid gland secretes that assist in regulating the body's cellular metabolic rate) concentrations; and

Total, free, and reverse triiodthyronine (T3, the other iodine-containing hormone secreted by the thyroid gland that assists in regulating the cellular metabolic rate of the body; much more powerful than T4, it is considered to be the active form of thyroid hormone in tissue) concentrations.

Sanchez said there were very little differed between the groups. The key difference the researchers found was between septic and sick nonseptic foals: all of the hormone levels were decreased in these animals, with the exception of reverse T3. Additionally, septic foals that did not survive had lower T3 and T4 concentrations than surviving septic foals.

"This decrease in thyroid hormones in ill foals appears similar to nonthyroidal illness syndrome, which is seen in ill human infants," Sanchez said. "The degree to which this occurs may be associated with severity of disease, but this point requires further study."

The next study she described also involved foals' HPA axis, but addressed the system's function after long-acting adrenocorticotropin hormone (ACTH) administration during the foals' first five days of life. Compared to pony foals receiving a placebo (saline), study foals' cortisol (stress hormone) concentrations at rest and in response to ACTH-stimulation were higher at three weeks post-administration but not at 13 weeks post-administration.

"Thus, it does not appear that rises in plasma cortisol concentrations during the neonatal period, such as in response to stressful events, reprogram the HPA axis in the relative short term," Sanchez said.

Previous studies in both humans and animals have linked abnormal programming of adult tissue function to excess glucocorticoids (such as ACTH) during perinatal development. So the researchers on the next study Sanchez described set out to determine if the same was true in foals.

Using 19 pony foals, the team found that glucocorticoid exposure (via ACTH administration) reduced foals' maximum plasma insulin response to a glucose challenge at both two and 12 weeks post-administration.

This is the first study to show altered pancreatic β-cell function after ACTH-induced glucocorticoid overexposure during early postnatal life in foals, which is interesting from a hormonal standpoint, Sanchez said.

Twelve foals were randomly assigned to a "vaccinated," "nonvaccinated," or control group. The researchers vaccinated the first group 60 and 30 days before experimentally infecting them with L. intracellularis. They also challenged the nonvaccinated group but didn't challenge the controls.

All of the vaccinated foals were protected from L. intracellularis infection, while three of the four nonvaccinated foals developed moderate to severe clinical signs of disease. None of the control foals developed EPE. The researchers noted no adverse effects in any of the vaccinated foals.

Sanchez said researchers are currently looking more closely at foals' response to vaccination.

Sanchez described one study about the effects of vaccinating mares prepartum against Clostridium difficile, a causative agent of enterocolitis—a sometime fatal disease in neonatal foals.

The researchers developed a vaccine against binding domain of Toxins A and B—important virulence (virus-causing) parts of C. difficile—and found that mares produced strong serum antibody responses after vaccination. Additionally, they identified high levels of toxin-specific antibodies in the mares' colostrum and in most of the foals' blood two days after suckling commenced.

"So while this vaccine is still in the developmental stages, it could be a way to help protect foals against this infection in the future," she concluded.

Next, Sanchez described a study that evaluated the most common pathogens associated with diarrhea in neonatal foals in Central Kentucky. The researchers examined 88 Thoroughbred foals, aged 2 days to 7 weeks, residing at 32 stud farms. The researchers tested fecal samples from 37 healthy foals and 51 with GI disease using a real-time PCR (polymerase chain reaction) assay.

They found that rotavirus was the most commonly identified pathogen, and that foals with salmonella or rotavirus identified in feces were more likely to have diarrhea than foals with other pathogens found. Additionally, the team found co-infections in many of the foals with rotavirus or salmonella.

"The study isn't earth-shattering, but it shows the importance of knowing what's likely to occur in your area," Sanchez said.

Moving forward, Sanchez described a blinded, placebo-controlled trial evaluating the efficacy of Saccharomyces boulardii—a type of yeast used in some probiotics—in treating antimicrobial-associated diarrhea in adult horses. The team found no difference in any parameters—including days to return to normal fecal consistency, resolution of watery diarrhea, attitude or appetite improvement, or survival at discharge, among others—between horses consuming S. boulardii or a placebo.

So is it worth while giving foals—or any horses, for that matter—with diarrhea this probiotic?

"We don't know," Sanchez said. "It didn’t seem to help or hurt horses in this study, and that is what (information) we've got for now."

Turning her attention fully back to foals, Sanchez described a recent study that evaluated progestogen derivatives in healthy and sick foals, and those with neonatal maladjustment syndrome (NMS).

The team found that healthy foals showed a significant decrease in pregnane (types of progestogen derivatives) concentrations over the first 48 hours of life, while ill foals, regardless of disease, had significantly increased pregnane concentrations. Concentrations of two pregnanes, progesterone and pregnenolone, decreased significantly in sick, non-NMS foals older than 48 hours, whereas concentrations in NMS foals remained increased, the team learned.

This research could help shed light on NMS, although whether these changes cause signs of or are a result of disease requires further study.

Sanchez described a study examining the prevalence of different bacteria isolated from septic foals from 1979 to 2010. Obtaining this information could help veterinarians better select antimicrobial drugs for foals' initial treatments.

They found that gram-positive isolates increased significantly over the years while, specifically, the percentages of Enterobacteriaceae (specifically Escherichia coli), and Klebsiella. spp. decreased. Additionally, Enterococcus spp. isolates were cultured more often in recent years.

The same researchers also completed an in vitro (in a laboratory) study on antimicrobial susceptibility patterns of bacterial isolates from septic foals over the same time span. They found:

Enterobacteriaceae, Actinobacillus spp., and β-hemolytic Streptococcus spp. showed an increasing resistance to gentamicin and amikacin over the aforementioned timeframe;

Enterococcus spp. became more resistant to imipenem and ticarcillin/clavulanic acid.

These results should help veterinarians on the West coast (the geographic region where the study was carried out) select the most effective antimicrobials for treating their neonatal patients, Sanchez said.

"The increased antimicrobial resistance noted in this study appeared mostly after 1997, which was associated with increased prophylactic administration of antibiotics to foals in the study region," Sanchez relayed. "Overall, results were similar to other recent reports showing that either ampicillin/amikacin, ceftiofur/amikacin, or ceftiofur alone are good first line choices. The results also reinforce the need for responsible antimicrobial usage."

About the Author

Erica Larson, news editor, holds a degree in journalism with an external specialty in equine science from Michigan State University in East Lansing. A Massachusetts native, she grew up in the saddle and has dabbled in a variety of disciplines including foxhunting, saddle seat, and mounted games. Currently, Erica competes in eventing with her OTTB, Dorado.

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